Investing method



Patented Sept. 20, 1949 UNITED STATES PATENT orrics INVESTING METHOD John Frel, In, Chicago, Ill.

Application November 9, 1944, Serial No. 2,707

2 Claims.

This invention relates to molds for use in casting various articles, and has to do with a method of investing patterns with mold forming material in the production of such molds.

It is known, particularly in the centrifugal casting art, to produce casting molds by investing heat destructible patterns, mounted in mold flasks, with a settable mold forming material in fluid form, permitting the investment material to set to the proper extent, after which the body of investment material and the pattern therein are properly heated so as to destroy and remove the pattern, thus providin a mold having a casting cavity therein conforming to the pattern. Much difllculty has been encountered in producing molds in this manner due, in large measure, to the presence of air in the investment material. This air frequently forms bubbles in contact with the pattern, with the result that the cast article has imperfections which in many cases render it unfit for its intended use. That is particularly true where precision is required.

Various attempts have been made to overcome the above referred to dimcuity resulting from the presence of air in the investment material. It has been proposed to invest the patterns by delivering the investment material to a stationary mold flask while the latter is within a space maintained under a suitable vacuum and, as soon as the flask has been properly filled, to admit atmospheric air to the space and thereby immediately relieve or break the vacuum. When the atmospheric air is admitted, the investment material is in a rather loose and unpacked condition, due to the effect of the vacuum, the air enters the space under considerable velocity and a portion of the entering air penetrates into the investment material. As a result, air is trapped in the investment material and a portion of this trapped air may, and frequently does, find its way to the pattern to which it attaches itself in the form of bubbles. This procedure oiiers no assured solution of the difliculty. It has also been proposed to subject a body of the investment material to a vacuum until ebullition ceases, immediately break the vacuum by admission of atmospheric air, carefully introduce the pattern into the investment material, subject the investment material with the pattern therein to vacuum and remove the pattern and let it set until the coating of investment material has hardened,

thereby providing it with a primary investment.

That operation may be repeated and the pattern with its coating of primary investment may then be subjected to a secondary investment in mate- 2 rial which has been subjected to vacuum in the same manner as for. the primary investment. Such a procedure obviously is time consuming and expensive. Also. it does not assure that all of the air is removed from the investment material, para secondary investment material. Here, again,

there is the difllculty that in introducing the pattern into the primary" investment air is also introduced and attaches itself to the pattern in the form of bubbles. Further, subjecting a mass of investment material to a vacuum, even when accompanied by vibration, does not suifice to remove all of the air from the material, particularly if the mass or body or investment material is of considerable depth, as is' frequently necessary. In such cases, the upper portion of the body of investment material 'will swell and bubble or boil and most of the air may be removed from that portion, but the lower portion of the mass will be but little aileted and most of the air originally present in the lower portion will remain there. Vibration of the mass causes packing, which retards escape of air from the lower portion thereof and aggravates rather than alleviating the condition which it is sought to remedy. None of the procedures above referred to has to my knowledge provided a satisfactory solution of the problem of removing air from investment material to be used'in the production of molds for casting, nor am I aware of any presently known procedure which accomplishes that desirable result in an assured and satisfactory manner.

My invention is directed to a method of investing patterns in a manner which avoids the above noted objections to the present methods and effectively guards against the presence of air bubbles in contact with the patterns. More specifically, I provide a method whereby a pattern may be completely invested in a single operation with assurance that no air bubbles will be formed in contact with the pattern. which efiects a material saving in time and work compared to the ble assured precision casting. Briefly, as to the method of my invention, 1 have discovered that by delivering the investment material to the mold flask while subjecting it to a vacuum effective for removing the air from the material, and pack- 3 ing the air free material about the pattern in the l 1 flask as it is delivered to the latter, the formation of air bubbles in contact with the pattern is completely eliminated. Preferably, whenthe flask 1', has been properly filled with the packed air free investment material, the vacuum is gradually reduced until the pressure to which the body of investment material is subjected has been increased to atmospheric. That avoids'risk of air entering the body of investment material, as might occur if the pressure were abruptly raised to ati mospheric and for that reason is desirable, though not essential to the broader aspects of the method of my invention. Further objects and advantages of my invention will appear from the detail del scription.

In the drawings: Figure 1 is a semi-diagrammatic view, partly 1 in section and partly in elevation, of investing means embodying my invention, illustrating also i the method of my invention; and.

Figure 2 is a view similar to Figure 1, but after completion of the investing operation and showing the bell jar in elevation and in its raised position.

I have shown, by way of example, preferred means for performing the method of my invention. This means comprises a suitable board or platform 5 hinged at one side, at G, to a suitable v support 1. ,A bracket 8 is secured to the underface of platform 5 adjacent and centrally of the 1 other side thereof, 1. e., the side opposite to its hinged side, and carries a roller 9 which contacts an eccentric l secured upon the shaft of an electric motor ll mounted upon a base |2,

which may be mounted upon support I below platform 5. Two tension springs |3 are anchored at their upper ends to platform 5, at the front and adjacent each end thereof, the lower ends of these springs being anchored to base |2. The platform is disposed horizontally and springs l3 hold roller 9 in pressure contact with eccentric l0 so that platform 5 is vibrated vertically when the motor II is in operation, the eccentric I0 being so formed that but slight vertical movement is imparted to platform 5.

A vacuum pump unit l4, of known type, has its intake connected by a length of flexible hose |5 to a tube It secured at its upper end portion through platform 5, this tube being provided with a suitable valve II of known type. A second tube I8 is secured to platform 5 and is connected to a vacuum gauge IQ of known type, this second tube being provided with a valve of known type. Preferably, though not-necessarily, a third tube 2| is secured to platform 5 and extends outwardly therebeyond, this third tube being provided at its outer end with a valve 22 of suitable known type.

The upper face of platform 5 is provided with a covering or pad 23 of rubber or other suitable material of a character to form a fluid tight seal with a flange 24 at the lower end of a glass cover a rubber stopper 2'! having a central opening for reception of a tubular neck or stem 28 of a glass funnel 23, neck 28 being controlled by a conical plug or cock mounted therein adjacent the lower end of funnel 28 and disposed a short distance above stopper 21. After the neck of funnel 28 has been inserted to the proper extent through stopper 21, the latter is pressed tightly into neck 26 of bell jar 25 so as to be compressed about neck 28, forming a fluid tight seal therewith and also gripping neck 28 frictionally, effective for supporting the funnel 29 in position, the stopper 2! also forming a fluid tight seal with neck26 of bell jar 25; as will be readily understood. Bell jar 25 is disposed between the depending arms of a frame or yoke 3| of elongated inverted U shape, in which yoke the bell jar is secured by thin metal straps 32 extending circumferentially about the bell jar and secured at their ends to the arms of yoke 3| by known means effective for drawing the straps 32 tightly about the bell jar. In that manner the bell jar 25 is secured in yoke 3| for movement therewith. A cable 33, preferably a wire cable, is suitably secured at one end to the upper end of yoke 3| centrally thereof, from which cable 33 passes over guide pulleys 34 and 35. A counterweight 36 is attached to the other end of cable 33 and tends to raise the yoke 3| and the parts carried thereby.

A stop 31 is suitably secured on the run of cable 33 extending between pulley and counterweight 36, the cable 33 below stop 31 passing between the 3|, together with the parts carried thereby, is-

raised by the counterweight 35, as will be understood.

The platform 5 is adapted for reception of a mold flask 4|] fitting tightly at its lower end in a flanged base 4| which has a flat underface and seats upon platform 5 within the area between the ends of the tubes l5, l8 and 2|, which are, of course, properly disposed to that end. The base 4| is provided with a central upwardly projecting element 42 having therein recesses for reception of the lower portions of one or more sprue pins 43. A frusto-conical element 44 is suitably secured to the upper ends of pins 43,

i this element and element 42 of base 4| tapering 3 of a suitable heat destructible material, such as i a low fusing alloy or a synthetic resin, wax, or I the like. Preferably, the pattern 45 and element 44 and the sprue pins 43 are formed of styrene, as separate elements, and are secured together by moistening appropriate areas thereof with a solvent, such as alcohol, so as to softenthem,

and pressing the surfaces together. Obviously,

1 erably is cylindrical and is formed of an alloy the elements referred to may be otherwise formed and secured together. The mold flask 40 prefsteel capable of. resisting high temperatures. The flask 40 is provided with a liner 46 of asbestos, or other suitable material of like character, which extends upward beyond the open upper end of settable refractory investment or mold forming The funnel 23 contains a suitable quantity of a material 41 in liquid form. Various investment suitable known investment material may be used in practicing my invention. I have found the investment material disclosed in Patent No. 2,027,932, issued to Arthur 3. R88. to be satisfactory. After the flask ll .with the pattern mounted therein as above has been properly positioned upon platform I, the bell jar 25 is disposed about flask 40 with flange 24 seating upon the rubber pad 23. The vacuum pump unit It is then set into operation and creates a'partial vacuum within the bell jar 2b, which is then held tightly seated upon platform 5 by atmospheric pressure. In the continued operation of unit H the appropriate degree of vacuum is produced within the bell jar 25 and, by proper adjustment of valve I1, is maintained. The degree of vacuum to be produced and maintained within the bell jar 25 need not be great and depends upon 1 the particular investment materialbeing used. The amount of vacuum should be sufficient to assure complete withdrawal of air from the. investment material without causing objectionable volatilization of liquid constituents thereof, andmay readily be determined by experiment. When the proper degree of vacuum within bell jar 25 has been attained, the stop cook is opened and the investment material 41 flows through neck 28 of funnel 29 and is delivered from the lower end of neck 28 into mold flask 40 through the open upper end thereof. As the stream of investment material is discharged from the lower end of funnel neck 28, it is exposed to the vacuum within bell jar which acts to break up or expand this stream radially so as to immediately remove all of the air therefrom, the investment material being then delivered to the flask 40 in more or less spray form instead of in the form of a solid stream. In that connection, it will be noted that the diameter of the entering stream of investment material is slight relative to the diameter of the mold flask lll, so that the vacuum maintained within the bell jar 25 is effective for spreading or breaking up the entering stream of investment material-and removing the air therefrom in the manner stated. At the time of opening the cook 30, or prior thereto, the motor I I is set into operation so that the flask i0 is vibrated during delivery thereto of the air free investment material. In that manner the investment material is freed of air and this air free material is packed in the mold flask about the pattern therein as it is delivered to the flask. After the flask 40 and the liner 46 has been filled with investment material to the proper depth, which is such that the investment material extends upward within liner 46 a material distance above the flask 40, the cook 30 is closed, it being noted that the amount of investment material in funnel 29 should be considerably in excess of the amount required for investing the pattern in the manner stated, so as to prevent entry of atmospheric air through the neck 28 of funnel 29 to bell jar 25. After the cock 30 has been closed, atmospheric air is admitted gradually to the bell jar 25 until the pressure therein becomes equal to atmospheric pressure, or but slightly lower than atmospheric. The admission of atmospheric air to the bell jar 25 may be through the tube 2| under control of valve 22, in which case valve I1 is closed, it being understood that the vacuum pump unit I is stopped when flask l0 and liner 48 have been filled to the proper depth with the investment material. Alternatively, the tube 2| may be omitted and valve ll may remain open 6 when unit I4 is stopped, slow leakage of air through unit l4 serving to gradually relieve the vacuum within the bell Jar 25. In either case,

the relief of the vacuum within the bell J'ar 25 should occupy a period of from 15 to 20 seconds. During that time the motor ll remains in operation and vibration of the flask 40 continues so that the investment material is firmly packed within the flask about the pattern before relief of the vacuum within the bell jar 25. In fact, the major portion of the investment material is firmly packed within the flask 40 by the time the latter has been filled to the proper depth and prior to closing of the cook 30. That obviates the risk of air entering the investment material within flask 40 to any appreciable depth, even though the vacuum within the bell jar be broken abruptly. Preferably, however, I usually break the vacuum gradually in the manner stated, as a further safeguard against possibe entry of air into the investment material within the mold flask. During the admission of air to the bell jar 25 for breaking the vacuum therein, or prior to breaking the vacuum within bell jar 25 in any other suitable manner, the investment material 41 within funnel 29 is replenished by an amount equal to that discharged from the funnel in the investing operation, all of the material within the funnel 29 being then stirred so as to assure uniform mix thereof. When the pressure within the bell jar 25 becomes equal to atmospheric pressure, or slightly less than atmospheric pressure, the counterweight 36 raises the yoke 3| and the parts carried thereby so as to position the bell jar 25 a proper distance above mold flask 40, as shown in Figure 2, so asto provide an unobstructed space above platform 5 for removal of flask 40 and the invested pattern therein, and for positioning upon platform 5 a second flask with a pattern therein to be invested. The bell jar 25 is then again seated upon the platform 5 and the operation is repeated. The automatic raising of the bell jar clear of the invested pattern and flask leaves the operators hands free and is conducive to expedition and facility in investing the patterns, of importance in quantity production.

After the pattern has been invested in the manner stated, the mold flask with the invested pattern therein maybe subjected to further vibra: tion for maintaining the investment material packed as it sets, and after the investment material has set to the proper extent the portion of the liner 46 above the flask 40 and the excess investment material therein is trimmed off. Thereafter the mold flask with the invested pattern therein is permitted to set until the investment material has properly dried, and the mold flask with the invested pattern therein is placed in a suitable furnace and heated to a temperature sufficient to destroy the sprue pins 43, the element 44 and the pattern 45, the mold flask being disposed at that time with the end having the pouring gate formed therein by element 42 of base 4! restricted openings provided by the sprue pins 43.

The mold formed in this manner constitutes the i casting mold and method, Serial No. 731,697 filed February 28, 1947, and need not be further described here, since the particular construction of I the mold'forms no part of my instant invention.

The mold may, of course, be of any other suitable construction within the broader aspects of my present invention.

subject matter of my copending application for l.

By delivering the investment material to the j mold flask in a stream subjected to a vacuum, 1 l the air is removed from the investment material and this air free material is packed in the mold flask about the pattern as it is delivered to the flask, whereby the possibility of air bubbles forming in contact with the pattern is eliminated. 1

While I have referred to the removal of air from the investment material, it will be obvious that 1 i the method of my invention is effective for removing gases other than air and which would tend to form bubbles in contact with the pattern, 1

Accordingly the term air" as used herein is to be construed as including air proper and other gases which like air would incur the risk of forming bubbles in contact with the pattern, and the term 1 air is used in that sense in the appended claims.

The removal of air or other gases from the lnvestment material in the manner explained above the production of the molds with a corresponding 3 saving in cost of production of the cast articles 3, while, as noted, assuring precision in casting of 1 associated elements have been destroyed and 3 the articles. After the destructible pattern and removed from the mold, as above, the heating of f the mold may be continued until it has been 1 raised to the proper temperature for casting, after which the casting operation may be performed in 'a suitable known manner.

As has been above indicated, and as will be understood by those skilled in this art, changes in details, may be resorted to without departing from the field and scope of my invention, and I intend to include all such variations, as fall within the scope of the appended claims, in this application in which the preferred form only of my invention has been disclosed.

I claim:

1. The method of investing a. pattern to make a casting mold which comprises mounting a pattern in a flask, investing the pattern with a settable mold-forming material by delivering to the flask a stream of said mold-forming material in fluid form, subjecting the stream to vacuum as it is being delivered to the flask so as to break up the stream and'remove air therefrom, and simultaneously vibrating the flask to cause a packing of the material about the pattern'and to release from the material any air entrapped therein, said air being drawn ofif byreason of the vacuum.

2. The method of investing a pattern to make a casting mold, which comprises mounting a pattern in a flask closed at its bottom and open at its top, placing the flask and pattern therein in an enclosure, producing a vacuum within the enclosure, investing'the pattern by delivering to the flask through its open top a settable refractory mold-forming material in fluid form in a downwardly flowing stream while maintaining said vacuum within the enclosure, thereby breaking up the stream and removing air from said material asit is delivered to the flask, vibrating said flask and the resultant air free material therein during delivery of the latter to the flask and while .it is subjected to the vacuum, thereby packing the material about the pattern and, following pouring of the mold, increasing pressure within the enclosure at a rate to prevent penetration by incoming air of the body of material packed in the flask.

J orm FREI, JR.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,320,770 Lougheed Nov. 4, 1919 1,325,004 Davidson Dec. 16, 1919 1,543,955 Sloan June 30, 1925 1,773,059 Ohno Aug. 12, 1930 1,805,970 Briggs May 19, 1931 2,065,977 Jefferies Dec. 29, 1936 2,092,832 Cohn Sept. 14, 1937 2,201,131 Jungerson May 14, 1940 FOREIGN PATENTS Number Country Date 53,934 Switzerland Dec. 24, 1910 

